Field of the Invention
The present invention relates to a process and an apparatus for building tyres for vehicle wheels.
More particularly, the invention applies to the process and equipment used for building a green tyre, to be subsequently submitted to a vulcanisation cycle for obtaining the final product.
Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads”, and having an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre for mounting on a respective rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers, arranged in radially superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. Applied at a radially external position to the belt structure is a tread band, of elastomeric material too, like other semifinished products constituting the tyre.
Respective sidewalls of elastomeric material are also applied at an axially external position, to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the “tubeless” type, an air-tight coating layer usually referred to as “liner” covers the inner surfaces of the tyre.
Subsequently to building of the green tyre carried out through assembly of the respective components, a vulcanisation and moulding treatment is generally performed which aims at determining the structural stabilisation of the tyre by cross-linking of the elastomeric compounds and also at impressing the same with a desired tread pattern and with possible distinctive graphic marks at the sidewalls.
The carcass structure and belt structure are generally made separately from each other in respective work stations, to be mutually assembled at a later time.
In document WO2008/099236 in the name of the same Applicant, a carcass ply is applied around an outer surface of a building drum, according to an application diameter greater than the fitting diameter of the tyre. Auxiliary support members, made in the form of two annular elements for example, can be removably moved close to the building drum on axially opposite sides. The auxiliary support members have respective rest surfaces preferably having a substantially cylindrical conformation of substantially the same diameter as the application diameter. The outer surface of the building drum has an axial size smaller than the width of the carcass ply, so that the end flaps of the carcass ply disposed on the building drum axially protrude from the opposite ends of the outer surface and are at least partly supported by the aforesaid rest surfaces. When formation of the carcass ply/plies has been completed, the auxiliary support members are axially moved away from the respective halves of the building drum, so that the rest surfaces can be removed from the carcass ply/plies and from other possible components applied thereto. Removal of the rest surfaces makes it possible to fold down the end flaps of the carcass ply/plies applied around the building drum, towards the geometric axis of said building drum. An annular anchoring structure defining the fitting diameter is coaxially engaged around each of the end flaps. An outer sleeve comprising at least one belt structure possibly associated with a tread band is disposed at a coaxially centred position around the carcass sleeve applied onto the building drum. Through axial approaching of the two halves forming the building drum, the carcass sleeve is shaped into a toroidal configuration to cause application of same against a radially internal surface of the outer sleeve.
In the technological context in which the Applicant has to operate, an increase in the daily productivity is often required for tyres that are different from each other in size and structure, while a high operating flexibility in the production is to be maintained.
More specifically, in this context by operating flexibility it is intended the possibility of using, for each tyre, elementary components that are different from each other in terms of type of elastomeric material or type of textile or metallic reinforcing cord.
In the present specification and in the following claims, by the term “elementary components” it is intended to denote continuous elongated elements of elastomeric material, rubberised textile and/or metallic cords, strip-like elements. To the aims of the present specification and the subsequent claims, it is to be pointed out that “strip-like element” means a strip of elastomeric material cut to size and comprising one or more textile or metallic reinforcing cords that are mutually parallel or crossed.
In the present specification and in the following claims by “component” of a tyre it is intended any part of the tyre or a portion thereof that is adapted to perform a function. For instance, intended as tyre components are the liner, underliner, abrasion-proof element, bead core, bead filler, carcass ply, belt layer, belt underlayer, tread underlayer, under-belt inserts, sidewall inserts, sidewalls, tread band, reinforcing inserts.
In this context the Applicant has verified that an excellent quality of the product can be achieved by manufacturing the whole green tyre without removing the carcass structure from the building drum, as described in the above mentioned document WO2008/099236.